Hydrothermal Performance of In-Tunnel Ground Freezing Subjected to Drilling Inaccuracy and Seepage Flow

Abstract

In the last few decades, artificial ground freezing (AGF) has been used as a temporary soil stabilization and waterproofing technique in geotechnical engineering, especially in tunneling construction. In construction, drilling inaccuracy of freeze pipes occurs, slowing the formation of a connected frozen wall and in turn undermining the process of AGF. This study used a hydrothermal coupling finite-element model to investigate the heat transfer and formation of a frozen wall during the progress of AGF. The simulation results indicate that the drilling inaccuracy causes temperature fluctuation at the temperature monitoring point and prolongs the formation time of the frozen wall. The maximum drilling inaccuracy allowed in practice is recommended to be 0.2 m based on the model (established using the shield tunneling of Nanjing Subway Line 10). The low-temperature zone develops unevenly and finally forms a complete frozen wall with an elliptical ring in the presence of the seepage flow. Thus, the location of the temperature monitoring points needs to be reconsidered, rather than being distributed evenly around the perimeter of the tunnel in practical engineering, and more monitoring points should be placed to monitor the formation of the frozen wall.